Bender type piezoelectric transducer



July 5, 1960 R. B. GRAY BENDER TYPE PIEZOELECTRIC TRANSDUCER Filed June20, 1955 QM K b BENDER TYPE PIEzoELE-crurc TRANSDUCER Robert B. Gray,Erie, Pa., assignor to Erie Resistor Corporation, Erie, Pa., acorporation of Pennsylvania Filed June 20, 1955, set. No. 516,638

24 'Qlairns. (Cl. ne -ream This invention is a piezoelectric transducerwhich pro- States tfim;

. in the same manner as barium titanate. Referring speduces lfrom asolid body ofpolarizable ferro-electric ceramic the response heretoforeobtained .from a bimorph made from two oppositely poled "bodies fixedtogether. By having take-oft electrodes at right angles to eachoth'erand to the direction of polarization, the transducer can beresponsed independently tomotions at right angles to eachother such aslateral and up and down motion. One use is in a binaural record playerwhere a single sound groove having both lateral and up and downformations can reproduce binaural sound effects.

The effects are obtained by polarizing the ceramic body along lines ofelectrostatic force which do not extend directly between oppositeelectrodes. For example, in a four electrode body having two pairs ofelectrodes at right angles to each other, the polarizing would be alonglines of force extendingbetween any two adjacent electrodes butnotbetween any pair of electrodes.

In the drawing, Fig. l is aside elevation of a tone arm and phonographpick-up for .a binaural record player; Fig. 2 is a top view; Fig. 3 is acircuit diagram of the binaural record player; Fig. 4 is a cross-sectionof a modified 'form of transducer element showing a possible orientationand position of the needle relative to the transducer element, and Fig.5 is a diagram showing the method of polarizing and a still further formof transduc'er element. 7

In'Figs. 1 and '2 of the drawing, there is. diagrammatically'shown tonearm 1 fixed atone end to a square piezoelectric ceramic bar 2. The otherend of the ceramic bar is tired to a holder 3 for a phonograph needle 1.When the needle 4 tracks in a sound groove having hill and daleformation, the needle moves'in the direction of arrow '5 causing theceramic bar 2 to bend in a vertical vplanemelative to the tone arm 1.'When the needle 4 tracks in a sound groove having lateralformation,.t'he needle moves in the direction ofthe arrow-6 and causesthe ceramic bar to bend, relative to the tone arm 1 in a lateraldirection. Since a record groove can contain both hill and dale andlateral formations, the pick-up is adapted to binaural record playerswhere the hill and dale formation in the sound groove is obtained fromone of two binaural microphones while the lateral formation in the samesound groove is obtained from the other of two binaural microphones. 'Inorder to obtain the binaural effect, the ceramic bar is provided withupper and lower take-oil electrodes 7 and 8.across which appears theoutput due to the up and down motion of the phonograph needle 4. Thisoutput is fed through an amplifier 9 to a speaker 10., The

lateral motion of the phonograph needle 4 produces an output whichappears across electrodes 11' and .12 on.

cifically to the upper and lower electrodes 7 and 8 as the needle 4moves up and down in the direction of the arrow 5, the ceramicfbar 2acts as a cantilever beam having tension stresses along one side andcompression stresses along the opposite side. Accordingly, if apiezoelectric response is to be obtained, the polarization of theceramic adjacent the electrode 7 should be opposite th'e polarization ofthe ceramic adjacent the electrode 8. Then tension stress adjacenttheelectrode 7 will produce the same response as the compression stressadjacent the electrode 8. If the polarization adjacent the electrodes "7and 8 were in the same direction, then the yol'tagegenerated by thetension stress at the electrode 7 would be equal and opposite to thevoltage generated by the compression stress adjacent the electrode 8 andthe two voltages would cancel out. This would result in no netpiezoelectric output. Because of the requirement of oppositepolarization, bender type piezoelectric elements have heretofore beenmade by sandwiching together two oppositely poled bodies.

As diagrammatically shown in Fig. 3 and also in Fig. 5, in the presentinvention the opposite polarization is obtained in a solid ceramic bodyby connecting the pola'r'izing voltage between adjacent electrodes. Thisproduces lines of electrostatic flux 15 and 16 extending respectivelyfrom the electrodes 11 and 12 Lo the electrode 7 and symmetrical linesof electrostatic flux l7 and 18 extending respectively from theelectrodes 11 and 12 to the electrode "8. It will be noted that thedirection of polarization indicated by the arrows on the electrostaticflux lines 15 to 18 inclusive is opposite at the electrodes 7 and 8 andis likewise opposite at the electrodes 11 and 12. Accordingly, in theregion of greatest stress, namely, adjacent the electrodes 8, 7, 11 and12 the polarization is in the proper direction for a response due tobending. Furthermore, it will be noted that because the electrodes 7, 8and .11, 12 are at right angles to each other, the .up and down movementof the needle produces an output only at the electrodes 7 and 8 whilethe lateral movement of the needle produces an output only at theelectrodes 11 and 12. Applicant, accordingly, produces in a solidceramic body a piezoelectric device having independent response tobending motions at right angles to each other.

The method of polarizing is illustrated in Fig. 5 where there is aceramic bar 19 of rectangular section having I electrodes 29 and 21 onits upper and lower faces. In

opposite sides of the ceramic'bar which output is fed 5 throughanamplifier 13 to a speaker 14. The separate speakers 1-0 and 14, whenspaced apart, reproduce the binaural sound resulting from theseparatelateral and hill and dale formations in the sound groove of therecord.

order topolar'ize this bar so that it will respond to bending in adirection normal to electrodes 26 and 21, the electrodes 20 and 21 areconnected to one side of a source 22 of polarizing voltage while metalelectrodes 23 and 2 4 which may be knife edges at opposite sides of theceramic bar and midway between the electrodes 20 and 21 are connected tothe opposite terminal of the source 22 of polarizing voltage. With thisconnection there results the electrostatic field indicated generally bythe arrows 25 which extend in opposite directions toward the electrodes2.0 and 21 and accordingly produce the proper polarization for responsedue to bending.

With the. rectangular shape shown in Fig. 5, the intensity oftheelectrostatic field is less midway between the electrodes 2.9 and 21than it is at the edges. Ac-

' 'cordingly, the polarization toward "the center of the elecofpolarization.

In Fig. 4 is shown another shape of ceramic bar which will producegreater output than the square or rectangular shapes illustrated inFigs. 3 and 5. This bar is of cross-shape section with electrodes 26 and27 on the upper and lower angular faces and electrodes 28 and 29 on theside faces. For polarization, the upper and lower electrodes 26 and 27are connected to one side of the polarizing voltage and electrodes 28and 29 are connected to the opposite side of the polarizing voltage.This produces the electrostatic field indicated by the arrows 30 whichit will be noted extends at right angles to the electrodes and inopposite directions for any pair of opposite electrodes. Accordingly,when the Fig. 4 ceramic bar is substituted in the tone arm of Figs. 1and 2, up and down movement causes a response to appear atelectrodes 26and 27, while the lateral movement causes the response to appear atelectrodes 28 and 29. Because the polarization is primarily on oppositesides of the arms 31 of the cross-shaped bar, the electrical capacitybetween the electrodes can be high and the polarization intensity can beuniform. From one aspect, the cross-shaped section of Fig. 4 makes thepolarization between any two adjacent electrodes more uniform and cutsdown the size of the dead space at the center of the body in which thereis a less intense or perhaps even an entire lack of polarization.

The Fig. 4 body may be described as having a center section with a pairof longitudinally extending flanges at the top and another pair oflongiutdinally extending flanges at the bottom and with the flanges ofeach pair projecting on opposite sides of the vertical center line ofthe center section of the body.

In each of the transducers, the area of each of the upper and lower andside faces of the ceramic body is large relative to the cross sectionalarea of the body transverse to the length of the body.

What is claimed as new is:

' l. A bender type piezoelectric transducer comprising an elongated bodyof polarized ferro-electric ceramic, said body having upper and lowerexterior faces and opposite exterior side faces connecting the oppositeedges of the upper and lower faces and each of the faces being of arealarge compared to the cross sectional area. of the body transverse tothe length of the body, a pair of longitudinally extending take-offelectrodes, one on each of the upper and lower faces, said body beingpolarized by an electrostatic field applied along the length of the bodyto at least one of said exterior side faces and diverging from betweensaid one exterior side face to the conducting electrodes, and meanssupporting the body at one end for bending .about an axis perpendicularto the length of the body and between the upper and lower electrodes.

2. A bender type piezoelectric transducer comprising an elongated bodyof polarized ferro-electric ceramic, said body having a center sectionwith a pair of longitudinally extending flanges at the top and anotherpair of longitudinally extending flanges at the bottom and with theflanges of each pair projecting on opposite sides of the vertical centerline of the center section of the body, the body having a pair of upperand lower surfaces including the upper and lower faces of the flangesand a pair of opposite side surfaces between said upper and lowersurfaces and including faces of the flanges on the sides of the flangesrespectively opposite said upper and lower faces of the flanges, a pairof longitudinally extending take-off electrodes, one on each of theupper and lower faces, and said body being polarized by an electrostaticfield applied along the length of the body and diverging from betweensaid opposite side surfaces to the electrodes on the upper and lowersurfaces.

3. The transducer of claim 2 in which a longitudinal ly extendingconducting electrode is applied to each of the opposite side surfacesand the body is polarized by an electrostatic field applied from theelectrodes on said side surfaces to the electrodes on the upper andlower surfaces.

4. A bender type piezoelectric transducer comprising an elongated bodyof polarized ferro-electric ceramic, said body having upper and lowerfaces and opposite side faces connecting the opposite longitudinal edgesof the upper and lower faces, a pair of longitudinally extendingelectrodes, one on each of the upper and lower faces of said body, andsaid body being polarized by an electrostatic field applied along thelength of the body and diverging from said opposite side faces of saidbody to the electrodes on the upper and lower faces.

5. The transducer of claim 4 in which a longitudinally extendingconducting electrode is applied to each of the opposite side faces ofthe body and the body. is polarized by an electrostatic field appliedfrom the electrodes on said side faces to the electrodes on the upperand lower faces.

6. A binaural pickup having a needle capable of simultaneously followingtwo record formations substantially at right angles to each other andproducing corresponding motions substantially at right angles to eachother, a bender type piezoelectric transducer comprising an elongatedbar of polarized ferroelectric ceramic symmetrical about two neutralaxes substantially at right angles to each other, means supporting oneend of the bar, means coupling the other end of the bar to the needle insuch orientation that the needle motion corresponding to one of therecord formations bends the bar about one of said neutral axes and theneedle motion corresponding to the other of the record formations bendsthe bar about the other of said neutral axes, a plurality oflongitudinally extending electrodes on the bar grouped in two pairs withthe respective pairs centered on axes at right angles to each other,said bar being polarized to produce an output in one pair of electrodes[in response to bending of the bar by the needle motion corresponding toone of the record formations, and said bar being polarized to produce anoutput in the other pair of electrodes corresponding to bending of thebar by the needle motion corresponding to the other of the recordformations.

7. A transducer having independent response to bending motionssubstantially at right angles to each other comprising anelongated barof'polarized ferro-electric material, said bar having a pair of oppositesurfaces transverse to one of the motions of response and another pairof opposite surfaces substantially normal to the first pair andtranverse to the other motion of response and connecting thelongitudinal edges of the first pair of surfaces, and each of thesurfaces of each pair being of area large compared to the crosssectional area of the bar transverse to the length of the bar, a pair ofelectrodes respectively on a surface of the pair normal to said one Adirection of response for receiving the outputfrom bending in said onedirection, another pair of electrodes respectively on a surface of thepair normal to said other direction of response for receiving the outputfrom bends ing in said other direction, and said bar being polarized bya voltage from one pair of electrodes to the other pair of electrodes.

8. A phonograph pickup comprising an elongated unitary bar of polarizedferro-electric ceramic, means supporting the bar at one end, a needlecoupled to the other end of the bar, said bar having a center sectionwith two pairs of longitudinally extending integral flanges projectingfrom the center section, one pair of flanges being on one side of alongitudinal center line of the body. and the other pair being on theother side of said center line, said bar being oriented with the flangestransverse to a component of movement of the needle whereby the bar andits flanges are bent in a direction transverse to the flanges by suchmovement, and a pair of takeeoff electrodes respectively on the outersurfaces of each pair of said flanges, said bar being polarized in onedirection at one of said electrodes and in the opposite direction at theother of said electrodes.

9. A phonograph pickup comprising an elongated unitary bar of polarizedferro-electn'c ceramic, means supporting. the bar at one end, a needlecoupled to the other end of the bar, said bar having a center sectionwith four substantially symmetrical angularly spaced longitudinallyextending integral flanges projecting therefrom, said bar being orientedwith the flanges transverse to a component of movement of the needlewhereby the bar and its flanges are bent in a direction transverse tothe flanges by such movement, and a pair of take-ofl electrodesrespectively on the outer surfaces of said flanges, said bar beingpolarized in one direction at one of said electrodes and in the oppositedirection at the other of said electrodes.

10. A transducer comprising an. elongated bar of polarized ferroelectricceramic, said bar having a center section with four substantiallysymmetrical angularly spaced longitudinally extending integral flangesprojecting'therefrom, said bar being symmetrical about each of twoneutral axes passing through the bar substantially at right angles toeach other and to the longitudinal axis of the bar, four electrodes eacharranged between two adjacent :flanges, and said bar being polarized inone direction at one electrode and in the opposite direction at the twoelectrodes adjacent said one electrode.

11. A transducer comprising an elongated bar of polarized ferroelectnicceramic, said barhaving a center section with four substantiallysymmetrical angularly spaced longitudinally extending integral flangesprojecting therefrom, said bar being symmetrical about each of twoneutral axes passing through the bar substantially at right angles toeach other and to the longitudinal axis of the bar, four angularlyspaced electrodes comprising two pairs with the electrodes in each pairon opposite sides of said bar, said bar being polarized in one directionat one electrode and in the opposite direction at the two electrodesadjacent said one electrode.

12. A transducer having independent response to bending motions abouttwo neutral axes substantially at right angles to each other comprisingan elongated unitary body of ferro-electric ceramic of the typepolarizable by an electrostatic field and with both of said axes passingthrough said body and said body being symmetrical about both of saidaxes, take-off electrodes on said body disposed on opposite sides ofeach of said axes, said body being polarized transverse to saidelectrodes and in opposite directions on opposite sides of each of saidaxes.

13. A phonograph pickup comprising an elongated unitary bar of polarizedferro-eleotric ceramic, means supporting the bar at one end, a needlecoupled to the other end of the bar, said bar having a center sectionwith two pairs of longitudinally extending integral flanges projectingfrom the center section, one pair of flanges being on one side of alongitudinal center line of the body and the other pair being on theother side of said center line, and a pair of take-off electrodesrespectively on the surfaces between the flanges of each pair of saidflanges, said bar being polarized in one direction at one of saidelectrodes and in the opposite direction at the other of saidelectrodes.

14. A phonograph pickup comprising an elongated unitary bar of polarizedferro-electric ceramic, means supporting the bar at one end, a needlecoupled to the other end of the bar, said bar having a center sectionwith four symmetrical angularly spaced longitudinally extending integralflanges projecting therefrom, and four electrodes, each electrode lyingon the adjacent surface of two flanges, and said electrodes beingsymmetrically disposed with respect to two axes substantially at rightangles to each other and passing between pairs of electrodes, and saidbar being polarized transverse to electrodes on opposite sides of saidaxes in the "sense to de velop voltage by bending abouteach of saidaxes.

15. A binaural pickup having a needle capable. of simultaneouslyfollowing record groove formations pro ducing motions substantially atright angles to each other, a bender type piezoelectric transducercomprising anelongated bar of polarized ferro-electric ceramic, said barhaving a center section with a pair of. longitudinally extending flangesat the top spaced substantially degrees apart and another pair oflongitudinally extending flanges at the bottom spaced substantially 90vdegrees apart and with the flanges of each pair projecting on oppositesides of the vertical center line of the center section of the bar, thebar having a pair of upper and lower surfaces including the upper andlower faces of the flanges and a pair of opposite side surfaces betweensaid upper and lower surfaces and including, faces of the flanges on thesides of the flanges respectively opposite said upper and lower faces ofthe flanges, said bar being supported at one end and coupled at theother end to the needle. with the upper and lower surfaces centered onan axis normal to the record groove, one pair of electrodes respectivelyon [the upper and lower surfaces, another pair of electrodesrespectively on the side surfaces, and said bar being polarized by avoltage from said one pair of electrodes to said other pair ofelectrodes.

16. A transducer comprising an elongated bar of polarized ferroelectricceramic, said bar being symmetrical about each of two neutral axespassing through the bar substantially at right angles to each other andto the longitudinally axis of the bar, four electrodes symmetricallydisposed on the bar, and said bar being polarized in one direction atone electrode and in the opposite direction at the two electrodesadjacent said one electrode.

17. A transducer comprising an elongated bar of polarized ferroelectricceramic, said bar being symmetrical about each of two neutral axespassing through the bar substantially at right angles to each other andto the longitudinal axis of the bar, a plurality of angularly spacedelectrodes on the bar arranged in two pairs with each pair symmetricallydisposed about a different one of said neutral axes, said bar beingpolarized one direction at one electrode and in the opposite directionat the two electrodes adjacent said one electrode.

18. A phonograph pickup comprising an elongated unitary bar of polarizedferroelectric ceramic, means supporting the bar at one end, a needlecoupled to the other end of the bar, said bar having a center sectionwith four substantially symmetrical angularly spaced longitudinallyextending integral flanges projecting therefrom, said bar being orientedso that at least two of the flanges are on opposite sides of the axisabout which said bar is bent by a component of movement of the needle,and a pair of take off electrodes on at least one of said two flanges,said bar being polarized in one direction at one of said electrodes andin the opposite direction at the other of said electrodes.

19. A phonograph pickup comprising an elongated unitary bar of polarizedferroelectric ceramic, means supporting the bar at one end, a needlecoupled to the other end of the bar, said bar having a center sectionand four electrodes, said electrodes being symmetrically disposed withrespect to two axes substantially at right angles to each other andpassing between pairs of electrodes, and said bar being polarizedtransverse to electrodes on opposite sides of said axes in the sense todevelop voltage by bending about each of said axes.

20. A piezoelectric transducer for producing an output in response tobending about each of two axes intersecting each other and normal to alongitudinal axis comprising an elongated unitary body of ferroelectricceramic of the type polarizable by an electrostatic field and of a shapesymmetrical about two neutral axes intersecting each other and normal tothe longitudinal axis of said body, said body having a pair of exteriorfaces respectively spaced on one and the opposite side of one of saidneutral axes and having a pair of exterior side faces respectivelyconnecting opposite edges of the first pair of faces, at least twolongitudinally extending conducting electrodes on said body, oneelectrode being on one face of the'first pair of faces and the otherelectrode being on the other face of the first pair of faces, and saidbody .being polarized by anelectrostatic field applied from at least oneof said side faces to the conducting electrodes, said field being of onepolarity at said one of the side faces and of the opposite polarity atsaid conducting electrodes.

21. A transducer as claimed in claim 20 in which the body has flangessymmetrically disposed on opposite sides of the axes of bending and thepolarization is transverse to said flanges. 22.-A transducer as claimedin claim 20 in which, in addition, a longitudinally extending conductingelectrode is applied to at least one of the opposite side faces and thebody is polarized by an electrostatic field applied from at least one ofthe electrodes on said side faces to the other electrodes.

23. A transducer as claimed in claim 22 in which the body has fourlongitudinally extending flanges and the electrodes are arranged on thesurfaces between adjacent flanges.

8 i 24; A transducer as claimedin claim 23 in'which the flanges aresymmetrically disposed to provide a body of cross shaped transversecross section.

References Cited in the file of this patent UNlTED STATES PATENTS Re.23,813 1 Adler Apr. 20, 1954 1,855,151 Jones Apr. 19, 1932 1,874,960Giebe et al. Aug. 30, 1932 2,025,388 Henning Dec. 24, 1935 2,439,499Williams et al Apr. 13, 1948 2,476,848 Eckhardt et al. July 19, 19492,515,446 Gravley July 18, 1950 2,841,722 Gravley July 1, 1958 2,880,334Mason -1 Mar. 31, 1959 2,900,536 Palo Aug. 18, 1959 FOREIGN PATENTS887,596 France Aug. 16, 1943 OTHER REFERENCES Marconi Review, vol. XVI,No. 111, page '150, Oetober 15, 1953.

